1. Field of the Invention
The present invention relates generally to the field of opposed crank arm chain drive systems, and more particularly to pedal drive mechanisms for bicycles, or other pedal-powered conveyances.
2. Description of the Prior Art
The first “bicycle”, comprised of two wheels, a seat, steering and pedals was produced in 1839 by Kirkpatrick MacMillan. Pedals were connected to a rear wheel by levers and operated in a reciprocating step fashion. In 1863 the first radial crank-powered pedal bicycle was invented by Pierre Michaux of France. In its design pedals were attached directly to a front wheel by crank arms. In 1874 the “high-wheeler” bicycle was introduced by James Starley of England. This bicycle design is well known for its large 60 to 80 inch front wheel and a small rear wheel. As with earlier designs, pedals of the high-wheeler were attached directly to the front wheel by crank arms. Handlebars were attached to the front wheel by a fork mated to a distinctive “S” shaped frame. The high-wheeler design allowed the rider to remain seated upright while providing power to the front wheel mounted pedals. In 1879 Harry Lawson introduced a rear wheel drive “bicylette”. His design was the first to use two wheels of the same size, a chain drive sprocket with pedals located under and slightly forward of the rider's seat and the standard “diamond” frame design still in use today. The pedal sprocket was connected to the rear wheel sprocket by a roller chain. Propulsion was provided to the rear wheel by the pedaling action of the rider.
Drive systems of some of the first bicycles used rigid wheel hubs. Eventually, the “coaster hub” design allowed the rider to pedal to maintain speed or coast without pedaling. Further advances in drive systems provided a variable speed transmission by augmenting the internal mechanism of the original coaster brake design. These transmissions were two or three-speed models controlled by a gearshift lever on the handlebars. Later, 10, 18 and 21-speed gear systems were introduced. The higher quantity gear systems used two or three different size chain sprockets attached to the pedal crankshaft and five, six or seven sprockets of different sizes attached to the rear wheel hub. A “derailleur” guided the drive chain from one size sprocket to another changing gear ratios as a result. An “S” shaped spring tensioning device attached to the rear wheel derailleur provided for differing lengths of slack in the chain during shifting. On most design versions, two derailleurs were used, one for the pedal (chain) sprocket and one for the rear wheel sprocket. Shifting was actuated by a cable link from the derailleur to a fixed position on the handlebars or the frame. Each derailleur would have its own shifting actuator.
In all previous pedal/crank arm/sprocket designs the pedal crankshafts would be 180 degrees opposed to each other ((the right pedal would be at top dead center (TDC) while the left pedal was at bottom dead center (BDC) or visa verse)). Because of the pedal/sprocket geometry and the position of the rider seated above the pedals, very little drive force could be applied when the pedals are within 10 degrees before and after TDC. Conversely, when the pedal cranks were both horizontal to the ground the rider could apply the greatest force to the sprocket drive chain system.
Over the last 100 years drive systems of modem bicycles have evolved to incorporate a set of opposed crank arms and pedals attached to a toothed (chain) sprocket which was attached to a central crankshaft and bearing on the bicycle frame. Power from the pedal/crank arm/sprocket assembly was transmitted to a bicycle's rear wheel sprocket by a roller chain. A rider obtains forward propulsion by applying downward force on one leading pedal (the power stroke) and then the other in reciprocating fashion in a forward moving rotation. Almost without exception chain sprockets, and wheel sprockets, have been radially symmetrical. The only exception was a recent innovation where the chain sprocket was designed in an elliptical pattern with the greatest radial pass of the sprocket teeth coinciding with the position of crank arms, thus increasing drive chain speed but not torque.
Inherent in a radially symmetrical pedal/crank arm/sprocket drive assembly is the portion of sprocket rotation where the opposed pedals are at TDC and BDC, and because of the relationship of the riders legs and feet to the pedals (similar to an internal combustion engine with the piston and crank shaft operation) there is little, if any, positive torque during this stage. Thus, the area of the pedal sprocket rotation where there is little or no positive torque is the rotation area of approximately 10 degrees before TDC and BDC, and 10 degrees after TDC and BDC. The present invention drastically reduces this mechanical deficiency.
Over the years many innovations have addressed various deficiencies of a bicycle's drive system. In June of 1977 a patent was issued (U.S. Pat. No. 4,029,334) for a step-type pedal drive system that allows the rider to propel a bicycle by pumping a set of reciprocating pedals instead of rotatively pedaling. This invention allows the rider to propel a bicycle by stepping on the pedals in a back-and-forth fashion instead pedaling in a rotative fashion found in the traditional pedal/crank arm/sprocket design of most modem bicycles. The deficiencies of this step-type drive system are the considerable number of components required in the mechanism itself and the fact that a completely new bicycle frame design would be required because this invention cannot be retrofitted to existing bicycle frames.
In July of 1979 a patent was issued (U.S. Pat. No. 4,159,652 a continuation-in-part of U.S. Pat. No. 3,906,807) for a bicycle drive assembly that permits the rate of pedal travel to be calculated and adjusted to more efficiently respond to pedal forces. This invention represents one of the first attempts at altering the opposed relationship of the pedals to eliminate the zero torque zones at top and bottom dead center of crank arm rotation. This was accomplished by relatively offsetting the centers of rotation of the chain sprocket (drive axis) and crank arms (power axis) and interconnecting them through a control mechanism and drive member to produce different rates of crank arm rotation speed. Because of the eccentric relationship between rotational centers of the chain sprocket and crank arms the power stroke crank arm (180 degrees of rotation on the forward most crank arm on a conventional bicycle drive mechanism) would decelerate and the return stroke crank arm (180 degrees of rotation on the aft crank arm) would accelerate thus eliminating dead centers at the top and bottom of each pedal stroke. The control mechanism allows the operator to vary the degree of eccentricity between the sprocket and crank arm centers thus varying the rate of acceleration and deceleration of the crank arms as they rotate through a pedal cycle. Principal deficiencies of this invention include its limited adaptability to all types of pedal-powered mass produced bicycles, its reliance on custom built recumbent style bicycle frames with complicated drive components to accommodate its intended increase in pedal efficiencies and its inability to use existing off-the-shelf bicycle components such as chain sprockets (chainrings), crank arm spindles, or axles (bottom bracket spindle/bearing sets) and standard pedals readily available at retail bicycle establishments.
In August of 1980 a patent was issued (U.S. Pat. No. 4,218,931) for a bicycle crank unit in which the chain wheel, or chain wheels, (chain sprockets) are eccentric with respect to the crank arm spindle (crank axle) and the crank axle carries an externally toothed pinion to engage within an internal gear carried coaxially by the chain sprocket. This provides a step down gearing between the pedal crank arms and the chain sprocket and enhances the mechanical advantages of the drive transmission. The singular advantage of this invention is to provide increase torque through an internal gear reduction system. The principal deficiency of this invention is that the same gear reduction and resulting increase in torque can be achieved through external chain sprockets and common gear derailleur systems available on almost all commercially available bicycles.
In November of 1987 a patent was issued (U.S. Pat. No. 4,706,516) for a radially movable pedal crank that provides greater rotational torque during the power stroke (when a rider applies force to the forward most pedal rotatively). This is accomplished by incorporating a series of eccentric plates, roller bearings and movable crank arms that when positioned on and around the bicycle crank sprocket would cause the crank arms to increase in radial length during the power stroke and decrease in radial length during the return stroke of pedal rotation. While this invention increases torque during the power stroke the rider's pedals have to cover a greater distance because of the increased circumference of a longer crank arm, thus requiring the rider to exert more effort to cover the same ground distance on the bicycle. Although the radially movable crank invention can be retrofitted to existing bicycle frames, a custom crank axle and bearing is required, components are numerous and heavy, and the assembly introduces considerable torsion and frictional forces in the drive system.
In May of 1996 a patent was issued (U.S. Pat. No. 5,515,746) for an eccentric traveling device which increases rotational torque without elongating the crank arms. This is accomplished by incorporating a chain sprocket rotatively mated to an eccentric plate, with its centerline aft of crankshaft centerline and a working plate attached to the crankshaft. The working plate, concentric to the centerline of the crankshaft and pedal crank, is connected to the chain sprocket by a set of five link arm assemblies rotatively positioned about the working plate. As the pedal/crank arm/working plate assembly rotates on the drive frame centerline (centerline of the crankshaft housing—“bottom bracket”) of the crankshaft, the rotative force is transferred to the chain sprocket, which has a center line aft of the crankshaft, to a roller chain and finally to the rear wheel. Similar to the radially movable pedal crank design described above, the eccentric traveling device can be retrofitted to existing bicycle frames. However, a custom crank axle and bearing is required, components are numerous and the assembly introduces considerable torsion and frictional forces in the drive system.
In July of 2000 a patent was issued (U.S. Pat. No. 6,085,613) for a crankset with no neutral position (top and bottom dead centers) consisting of a fixed bottom bracket tube, two opposed crank arms attached respectively to a hollow outer spindle mounted by bearings over a solid inner spindle. This spindle set includes a pair of output crank arms that transfer force from the pedals to the sprocket by way of articulating connecting rods. The axis of the crank arms (first axis) are offset from that of the chain sprockets (second axis) which are rotating on bearings mounted to the bottom bracket housing by an eccentric plate. With two rotating eccentric centers, the crank arms, the first axis of input, will accelerate and decelerate simultaneously as they rotate given a constant rotation speed of the sprockets, the second axis of output, causing the elimination of top and bottom dead centers. Eccentric drives such as this rely on bearings at the connecting points to help transfer force from the pedals to the chain sprockets. To reduce bearing wear caused by road hazards all bearings are sealed by contact gaskets. While of sufficient design this invention may experience questionable marketability because of its complicated design, reliance on a custom built bottom bracket housing and a considerable amount of additional bearings and gasket seals required to transfer power from the pedals to the chain sprocket. Also, the increased weight, friction and resistance introduced by additional bearings and gasket seals (a conventional pedal drive mechanism has four bearings and two gasket seals within the bottom bracket housing, this invention has thirteen bearings and seven gasket seals) will most likely overcome any mechanical advantage produced by this invention's design.
The present invention corrects many of the principal deficiencies apparent in aforementioned designs. First conceptualized in 1949, the present invention evolved over the years to its current embodiment so designed that a bicycle rider can continually apply force to the drive system without any interruption caused by simultaneous positioning of pedal cranks around top and bottom dead centers of the pedal rotation of a conventional pedal drive mechanism. The present invention incorporates lightweight materials, fasteners and low friction sealed bearings to minimize additional weight and rotational resistance.